Devices for preventing the unwinding of thread from a spool are very old in the patented art. Up to the present, however, such devices have not, as far as applicant is aware, gone into use or even become available in the marketplace.
Since, for best results, each spool of thread in a sewing room should be equipped with a keeper, it follows that (1) the keeper should be small and uncomplicated so as not to increase appreciably the required storage space and (2) the cost should be low to minimize the initial purchase price of the quantity needed to equip all spools of which there might be several dozen in a typical household sewing room.